1. Field of the Invention
The invention relates to a thin film magnetic head and a magnetic recording apparatus such as a magnetic disk drive, and more particularly to a thin film magnetic head having a small flying height just above a magnetic recording medium and to a magnetic recording apparatus.
2. Description of the Related Art
A magnetic hard disk drive (HDD) has a magnetic head (slider) 1 with a thin film magnetic head as shown in FIG. 12. The magnetic head (slider) 1 shown in FIG. 12 has an Al.sub.2 O.sub.3.TiC substrate 2 with an insulation layer of an AlO.sub.x film 3 disposed on its main surface.
Slider parts 4 are disposed on both sides of the Al.sub.2 O.sub.3.TiC substrate 2 at a medium opposed face side. The medium opposed face of the slider part 4 is called an ABS (Air Bearing Surface) by which the magnetic head slider 1 flies above a magnetic disk. A reproducing element or/and recording element 5 (transferring element) is disposed inside the AlO.sub.x film 3. The reproducing element or/and recording element 5 is a so-called thin film magnetic head that transfer information to and/or from the magnetic disk. Reference numeral 6 in FIG. 12 denotes a coil for supplying a recording magnetic field to the reproducing element or/and recording element 5. The reproducing element or/and recording element 5 is disposed in one of the slider parts 4 in view of the direction in which a medium is running and a production process thereof.
The magnetic recording apparatus such as HDD is highly demanded to record information in a high density. To achieve the high recording density, techniques for providing a narrow track width and a short gap are essential. For example, a HDD having a recording density of 200 Mb/inch.sup.2 (bpsi) has a recording track width of 7 .mu.m and a track pitch and a track width tolerance of about 2 .mu.m. To have a recording density of 1 Gbpsi or more, particularly 5 Gbpsi or more, it is demanded to have a recording track width of 3 to 5 .mu.m or below and a track width tolerance of 0.5 .mu.m or below.
With a higher density of recorded information, a signal magnetic flux quantity is lowered. For a compensate of the lowered signal magnetic flux quantity, it is necessary to decrease a flying height of the magnetic head above the magnetic recording medium. The flying height of the conventional magnetic head changes to 100 nm or below. Especially, the flying height of the magnetic head is required to be 50 nm or below when a recording density is 1 Gbpsi or more, and 20 nm or below when it is 5 Gbpsi or more.
For a reproducing head, a magnetic head (MR head) to which a high sensitive magnetoresistance effect element (MR element) is applied is being used to compensate the lowered reproducing output due to the reduction of recording track width. FIG. 13 shows the structure of a shield type MR head to be used as a reproducing potion of the reproducing element or/and recording element 5.
A lower magnetic shield layer 11 made of Permalloy or the like is formed on the main surface of the Al.sub.2 O.sub.3.TiC substrate 2 through an AlO.sub.x film 3'. The Al.sub.2 O.sub.3.TiC substrate 2 is a substrate configuring the magnetic head slider 1. A magnetoresistance effect film (MR film) 13 is formed on the lower magnetic shield layer 11 through a nonmagnetic insulation film 12 configuring a reproducing magnetic gap. An MR element 14 comprises the MR film 13 and a pair of leads 15 connected to both ends of the MR film 13.
An upper magnetic shield layer 17 is disposed on the MR element 14 through a nonmagnetic insulation film 16 configuring a reproducing magnetic gap. Thus, the shield type MR head is configured as the reproducing potion. To detect a signal magnetic field by the shield type MR head, a sense current is fed through the pair of leads 15 and the element resistance of the MR film 13 is measured.
A recording part of the reproducing element or/and recording element 5 is formed following the upper magnetic shield layer 17. The recording part has a pair of upper and lower magnetic poles (not shown) which form a magnetic circuit through a recording magnetic gap. The coil 6 produces a recording magnetic field between the pair of magnetic poles. An insulation protective film such as an AlO.sub.x film is formed on the recording part. This insulation protective film forms a part of the AlO.sub.x film 2.
A HDD which uses an ABS to fly the magnetic head slider 1 above the magnetic disk does not seem to have a problem that the magnetic head slider 1 comes in contact with the magnetic disk. However, contact between the reproducing element or/and recording element 5 and the recording medium occurs due to surface roughness, which are called a glide height, formed on the surface of a recording medium. This contact becomes conspicuous as the flying height of the magnetic head slider 1 is made small. The contact between the reproducing element or/and recording element 5 and the recording medium induces a local temperature rise on the MR film 13. When the temperature of the MR film 13 rises, a reproducing voltage output level is varied, and a readout error which is designated as thermal asperity occurs.
In addition, the reproducing part using the MR element 14 has a temperature increase of about 40.degree. C. due to a sense current (up to 5 mA) for measuring a resistance change. At an ambient temperature of 80.degree. C., the temperature of the MR element 14 rises to about 120 to 130.degree. C. This temperature increase of the MR element 14 results in interface diffusion of the MR film 13 and property deterioration of the magnetic layer forming it in the long view.
When the flying height of the magnetic head slider 1 is determined to be about 20 nm or below which is a smoothing limit of the recording medium, a contact probability between the reproducing element or/and recording element 5 and the recording medium is dramatically increased. Also, the disposition of the reproducing element or/and recording element 5 on one side of the magnetic head slider 1 is a cause of increasing the contact probability between the reproducing element or/and recording element 5 and the recording medium. Thus, the magnetic head and the magnetic recording medium are contacted in a broad area including the neighborhood of the MR film 13.
And, deviated abrasion is caused when the AlO.sub.x film 2 or the like having small hardness is exposed to the medium opposed face of the magnetic head contacting in a large area. The deviated abrasion of the medium opposed face increases a space between the magnetic head and the recording medium, resulting in degrading the recording resolution and reproducing resolution. If wear is substantial, the component materials positioned inward of the medium opposed face are exposed sequentially. Particles of a lubricating layer of the recording medium are adsorbed, also causing abrasion of the lubricating layer. The magnetic head slider 1, which has the reproducing element or/and recording element 5 disposed on one side, also has a disadvantage that trace precision of the recording tracks tends to be lowered when the recording density is made high.
For a head structure which does not involve a direct contact between the MR film and the recording medium, there is proposed a yoke type MR head which flows a signal magnetic field to the MR film through the magnetic yoke (see JP-A-08-138,215). For example, the yoke type MR head has a pair of magnetic cores which become the magnetic yoke disposed on an Al.sub.2 O.sub.3.TiC substrate through an insulation film. The pair of magnetic cores are disposed through a magnetic gap so to form the same plane. And, the MR element is disposed on this flat type magnetic yoke. The coil of the recording part is formed to have the magnetic yoke made of a pair of magnetic poles.
The magnetic head slider using the yoke type MR head has the width of ABS of the slider part having the reproducing element or/and recording element determined to be narrower than the width of ABS of the other slider part. And, the flying height of the slider part having the reproducing element or/and recording element is determined to be smaller than that of the other slider part. Thus, the leading end of the reproducing element nearly or/and recording element comes into contact with the recording medium.
A magnetic head slider using the yoke type MR head described above has a possibility of causing the same disadvantage as the magnetic head slider using the shield type MR head. Besides, since the yoke type MR head has the pair of magnetic cores disposed in a horizontal direction, the reproducing element or/and recording element exposed to the medium opposed face is thinner than the shield type MR head. The MR film has a disadvantage that reproducing element or/and recording element is worn more easily though the MR film is not directly exposed to the medium opposed face.
As described above, when the magnetic head slider is flying slightly while running, the reproducing element or/and recording element which is exposed to the medium opposed face produces heat due to the contact with the recording medium, inducing a thermal asperity. Properties are also degraded by the temperature increase due to the sense current supplied to the MR film. Therefore, it is highly demanded to improve heat dispersion in the neighborhood of the reproducing element or/and recording element including the MR film.
Besides, if the flying height of the magnetic head slider lowers to the smoothing limit or below of the recording medium, wear occurs in a wide area in the neighborhood of the reproducing element or/and recording element, and recording and reproducing resolution is degraded. If wear is substantial, the lubricating layer of the recording medium is also worn. Therefore, it is desired that wear in the neighborhood of the reproducing element or/and recording element is retarded when the magnetic head slider is being slightly while running.
The magnetic head slider having the reproducing element or/and recording element disposed on one side is a cause of increasing a contact probability between the reproducing element or/and recording element and the recording medium. Furthermore, when the recording density is highly increased, trace precision of the recording tracks is degraded. Under the circumstances, a technique for providing a stable running of the magnetic head slider is demanded.